Synthetic filaments having at least three continuous nonround voids

ABSTRACT

A YARN OF CONTINUOUS FILAMENTS SPUN FROM A THERMOPLASTIC POLYMER THROUGH SEGMENTED ORIFICES. EACH OF A LARGE PERCENTAGE OF THE FILAMENTS HAS AT LEAST THREE CONTINUOUS VOIDS, A VOID CONTENT OF ABOUT 10-35% AND AN EXTERIOR SURFACE FREE FROM ANY APPRECIABLE CONCAVITY. THE YARN GIVES A GOOD YIELD AND IMPROVED SOILING PERFORMANCE.

United States Patent Ofice Patented July 10, 1973 US. Cl. 161-178 5 Claims AESTRACT OF THE DHSCLOSURE A yarn of continuous filaments spun from a thermoplastic polymer through segmented orifices. Each of a large percentage of the filaments has at least three continuous voids, a void content of about -35% and an exterior surface free from any appreciable concavity. The yarn gives a good dye yield and improved soiling performance.

This is a continuation-in-part of our copending application Ser. No. 802,414, filed Feb. 26, 1969, now abandoned.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention concerns novel synthetic filaments which provide in fabrics an improved combination of filament bulk, covering power, soiling performance, luster and dye utilization (dye yield).

(2) Description of the prior art The bulk, covering power, soiling performance and luster of solid filaments can be improved with little loss in dye yield by the use of certain trilobal cross-sections as described in US. Pat. 2,939,201. Much greater improvements in soiling performance can be obtained with round filaments containing numerous microscopic discontinuous voids throughout their cross-section as described in US. Pat. 3,329,557; however, such filaments compared to solid trilobal filaments provide less bulk (due to a more compact filament cross-section), have less luster and suffer a considerable reduction in dye yield.

An object of this invention is synthetic textile filaments which provide in fabrics an improved combination of filament bulk, soiling performance, luster and dye yield along with good resistance to wear as encountered in upholstery fabrics and textile floor covering materials.

SUMMARY OF THE INVENTION The invention is a textile filament of substantially uniform cross-section throughout its length, melt-spun from a thermoplastic, synthetic polymer and characterized by having at least three continuous, nonround, substantially equidimensional, equispaced and parallel voids extending throughout its length, said voids comprising from about 10% to about 35% of the filament volume, and said filament having a cross-sectional contour substantially free of re-entrant curves throughout its periphery. Except for the equispaced voids, the filament is solid with a solid axial core.

The phrase substantially free of re-entrant curves" means that the filament contour is relatively smooth and substantially free throughout its periphery of any crosssectional bulges or depressions of suificient magnitude to provide an enclosed region or pocket for entrapment of soil when the filament is in side-by-side contact with other filaments, e.g., abrupt radial departures and bulges produced by the use of post-coalescent spinneret orifices employing slots with overlapping ends and the use of spinneret orifices which give lobed filaments having concave sides. Stated otherwise, the filament sides may be substantially round, convex or flattened but not appreciably concave.

The term soiling performance refers to the apparent resistance of a textile material to visible soiling which may be independent of the soiling which actually occurs.

The term dye yield refers to the apparent depth of shade for a dyed textile article at a given dye concentration in the article. A lower dye yield means that the material appears visibly lighter in dye shade at the same dye concentration as a similar material having a higher dye yield. Obviously, the higher the dye yield, the less the dye concentration needed to achieve a given depth of color, which is of significant economic value in the textile trade.

DESCRIPTION OF THE FIGURES In the drawings, FIG. 1 depicts an enlarged view of a spinneret orifice suitable for melt-spinning otherwise solid filaments containing four, substantially equidimensional and equispaced, parallel continuous voids; FIGS. 10:, b and c are enlarged sectional views taken from photomicrographs of nylon filaments spun through orifices of the type shown in FIG. 1; FIG. 2 is an enlarged sectional view taken from a photomicrograph of a nylon filament spun through an orifice similar to FIG. 1 except for omission of one segment; and FIG. 3 is a similar view of a filament spun from polyethylene terephthalate, through an orifice of rectilinear segments.

Filaments of this invention may be prepared from synthetic, linear, thermoplastic polymers which are meltspinnable. Among the more important polymers are the polyamides such as poly(hexamethylene adipamide), poly(caproamide) and polyamides of bis(4-arninocyclohexyl)methane and linear aliphatic dicarboxylic acids containing 9, l0 and 12 carbon atoms; copolyamides; polyesters such as the condensation products of ethylene glycol or tetramethylene glycol and terephthalic acid and copolymers thereof; polyolefins such as polyethylene and polypropylene. Both heterogeneous and homogeneous mixtures of such polymers may also be used.

The filaments can be prepared by known methods for spinning hollow filaments. Molten polymer is spun through spinneret orifices shaped to provide the desired number of voids and filament cross-section under spinning conditions which give the desired denier and percent void. Specific spinning conditions and spinneret orifice shapes and dimensions will vary depending upon the particular polymer and filament product being spun.

The number of voids is dependent on the design of the spinneret orifice. Percent void is mostly dependent upon the spinning and quenching conditions. Normally, the percent void can be increased by more rapid quenching of the molten filaments and by increasing the polymer melt viscosity.

Both pro-coalescent and post-coalescent spinnerets and spinning techniques can be used. The former requires injection of a gas or blowing agent into the molten polymer prior to spinning to maintain the void structure, whereas the latter involves entrapment of gas by coalescence of the molten polymer upon exiting from a segmented orifice.

Post-coalescent spinning is generally preferred for pro ducing filaments of this invention, because of the simpler process conditions, using segmented spinneret orifices of the type shown in FIG. 1. With such orifices, the number of slot segments with spokes determines the number of continuous voids produced in the filaments provided their dimensions and the spinning conditions are adjusted to give good coalescence. Similar orifices which employ overlapping slot ends for improved coalescence are generally not satisfactory because of their tendency to give abrupt radical departures and bulges in the filament crosssection which are detrimental to soiling performance as described herein.

With orifices of the type shown, there is a tendency for the sides of the resulting filaments to become flattened, during the coalescence process, as compared to the overall shape of the orifice. This flattening, which is accentuated as the void content is increased, can occur to such an extent that the sides of the filaments become concave, that is, reentrant curves are introduced into the contour of the filament. Consequently, this tendency must be counteracted by altering the shape of the peripheral slots or altering slot dimensions to feed a relatively greater portion of polymer to the solid, axial core of the filament, for example, by increasing the width of the radial slots or spokes, other conditions remaining constant. The resulting smooth exterior surface has been referred to herein as being substantially free from reentrant curves or appreciable concavity or abrupt radial departures or as free from substantial re-entrant curves. In these respects, the filaments shown in FIG. lc have substantial re-entrant curves and gave a relatively poor soiling performance.

The voids comprise from about to about 35% of the volume of the filaments of this invention. Soiling performance decreases rapidly at lower void contents. Soiling performance increases only relatively gradually as the void content increases from about 10 to about 25% with substantially no improvement in soiling occurring above about 25 void. Soiling performance remains substantially constant from about 25% up to about 30% void. Much higher void contents are difficult to produce and tend to weaken the filaments significantly under severe use.

When a bright filament luster is desired, the filaments of this invention preferably have flattened sides, for example, triangular or quadrilateral-like cross-sections with rounded or flattened sides and rounded corners.

Applications for which the filaments of this invention are highly useful normally require a denier per filament (d.p.f.) within the range of about 7 to about 25. For example, for indoor, residential and commercial carpets a d.p.f. of from about 12 to 20 is usually preferred. The optimum denier is determined by the aesthetics and performance desired for the particular use intended.

The filaments may contain conventional polymer additives for synthetic textile filaments such as antioxidants, light stabilizers, dyes, delustering agents, antistatic agents, etc., which may be incorporated in the polymer before, during or after polymerization and spinning. For maximum brightness of luster the filaments should contain less than about 0.5% of an opaque pigment at which level the amount of pigment is not great enough to significantly hinder the transmission of light through the filaments.

Generally the filaments of this invention will be subjected to a crimping or texturing treatment prior to use. Conventional crimping and texturing processes may be employed such as gear crimping, heated stutfer-box crimping and hot, fluid jet texturing. Although some crushing of the hollow filaments may occur in mechanical crimping processes such as gear crimping and heated stutter-box crimping, this is generally not detrimental to their subsequent performance.

EXPERIMENTAL TEST METHODS EMPLOYED IN THE EXAMPLES (A) Percent void determination Percent void is conveniently determined by measurement of filament density as compared to the density of a solid filament of the same polymer. A length of yarn weighing from about 6 to 8 grams is seared gently on each end with a flame to seal the filament ends. The exact weight of the yarn is determined. The density of the yarn is determined by a conventional liquid pycnometer method. In the following examples the liquid used in the pycnometer is carbon tetrachloride maintained at a temperature of 26:0.1" C. in a constant temperature bath. The density of a control solid filament yarn is also determined. Percent void is then calculated by subtracting the density of the hollow filament yarn from the density of the control, dividing the result by the density of the solid filament yarn and then multiplying by 100. In the following examples a density value of 1.09 is used as the density of solid filaments of poly(hexame'thylene adipamide).

(B) Competitive floor soiling test Floor soiling test results (overall rate and severity of soiling) vary with seasonal weather conditions, e.g., inclement weather results in heavier and more rapid soiling. To minimize these variations and more uniformly simulate results under inclement weather conditions, the test carpet items, immediately before testing, are uniformly sprayed twice with a light coat of a commercial brand of penetrating oil. The volatile oil is composed of a light lubricating oil combined with petroleum distillates. The oil is sprayed using a simple insect sprayer. The oil merely allows the soil to cling initially to the filaments as is the case when the carpets are soiled with snowy or muddy shoes.

Strips of carpet sections to be tested are laid on the floor of a heavily traveled industrial plant corridor. The number of cycles (times stepped upon) is measured by a pressure sensitive pad fastened under the carpeting and attached to a counter. The counter is activated only when the carpet above the pad is stepped upon. The carpet strips can vary in width from about 1 to 6 feet and can be up to 10 feet long. A convenient test size for each test item is about 12 inches (30.48 cm.) square. After the desired number of cycles, the carpets are cleaned by a standard vacuum cleaner. After cleaning, reflectance measurements are made on the different test carpet sections with a Model 610 Photovolt Reflectometer using a green tristimulus head. Readings are taken at equally spaced intervals over the entire carpet section and then averaged for determination of theK/S value for each item being tested, where the subscript s denotes a soiling test reading. If especially soiled areas or clean areas or clean areas are observed these are averaged in with the overall readings. The K/S values are then calculated using the following equation:

where K is the absorption coeflicient, S is the scattering coeflicient and R is the reflectance of an infinitely thick sample. Lower K/S values reflect a less solid appearance. Since the rate of soiling will vary from time to time, depending upon weather conditions, traffic, etc. it is essential that for a given comparison series, all carpet items be tested simultaneously in order to obtain a meaningful comparison of the test results.

Before soil testing the carpet sections are mock dyed as follows:

The carpet samples are placed in a cold water solution which contains 20 ml. of NH OH and 20 ml. of a 10% Merpol HCS solution per gallon of water. A solution to carpet ratio (by weight) of 40:1 is used. The bath is raised to C. and held at that temperature for one hour. The carpets are rinsed three times with cold water, centrifuged and allowed to dry in the air.

(C) Polymer relative viscosity Relative viscosity of the poly(hexamethylene adipamide) of the examples is determined in a conventional manner using an 8.4% by weight solution of polymer in 90% formic acid at 25 C.

ance compared after 15,000 cycles. Results are shown in Table IV.

(D) Polymer flow rate TABLE IV It K Flow is calculated from orifice area as follows: 5 bs a B 1.30 K c 1.51

where K and N are constants, b is orifice width and a is orifice length. Thus the flow rates in the peripheral and radial segments of the spinneret orifice are proportional to the product of the slot length and slot width to the third power.

EXAMPLE Carpet soiling performance of three 66-nylon yarns of hollow filaments containing 4-voids is tested to observe the effect of re-entrant curves in the filament cross-section on soiling performance.

The filaments of all three items are melt-spun from poly(hexamethylene adipamide) containing 0.15% Ti0 delusterant using slotted spinneret orifices having a configuration as shown in FIG. 1; however, average slot dimensions for the three items differ as shown in Table I.

Spinning and bulking conditions are shown in Table II. The yarns are spun, drawn and bulked (textured) with a hot-air jet in a continuous operation. A heated roll is used to pre-heat the yarn prior to the bulking operation. A hot air, jet-bulking process of the type described in US. Pat. 3,186,155 is used. In order to obtain the desired high percent void, it is found necessary to increase the cross-flow, quenching air flow near the spinneret as compared to the spinning of similar solid filaments on the same spinning apparatus.

Filament and yarn properties are shown in Table III.

Two yarn ends of Item A are plied to give a total yarn denier equivalent to Items B and C. Tufted level-loop As seen in Table IV, Items A and B are superior in soiling performance to Item C. Visual comparison of the soiled carpets shows Item A to have a slightly less soiled appearance than B and both A and B appear less soiled than C.

Examination of photomicrographs of multifilament yarn cross-sections prepared in a conventional manner show that some of the filaments do not coalesce properly, resulting in a collapsed or undersize void, or an open void. However, more than half of the filaments have a crosssectional contour substantially free of re-entrant curves for Items A and B, whereas filaments of Item C have cross-sectional contours with substantial re-entrant curves, as seen in FIGS. 1a, lb and 10, respectively. The otherwise solid filaments of preferred Item A have a substantially quadrilateral cross-section with rounded corners and four, substantially equidimensional, equispaced, continuous, parallel, quadrilateral voids throughout their lengths.

In another comparative test, carpets of similar construction were tufted from three filamentary yarns spun from polyhexamethylene adipamide. The otherwise equivalent yarns contained filaments with one central, three and four, substantially equidimensional, equispaced, continuous, parallel voids, respectively. It was readily ap parent to the naked eye that the three and four void items exhibited superior soiling performance. Test results showed equivalent dye yields, i.e., the improved soiling performance was realized with no penalty in dye yield performance.

In still another test, the recoveries from compression TABLE I Slot width Slot end spacing Polymer flow rate I (gr./min.) Diameter Peripheral Radial Peripheral Radial Fl ti Peripheral peripheral/ In. (Mun) In. (Mm.) In. (Mm.) In. (Mm) In. (Mm) slots Radial slots radial 0. 080 (2.0) 0. 0031 (0. 079) 0. 0026 (0.066) 0.0085 (0. 22) 0. 015 (0.38) 0. 49 O. 15 3, 3 0. 080 (2. 0) 0. 0034 (0. 086) 0. 0024 (O. 061) 0. 0086 (0. 22) 0. 015 (0.38) 0. 0. 12 5. 4 0. 081 (2.1) 0. 0030 (0.076) 0.0018 (0. 046) O. 0075 .19) 0. 014 (0. 36) 0. 45 0.05 8. 8

TABLE II Air let Spinneret Polymer throughout Pressure block Draw Hot roll 'Iemp., Item temp., C. lb./hr. kg./hr. ratio temp., 0. C. p.s.l. (kgJcmfi) B For 160 filaments; bundle is split before drawing and wound up as two 80-filarnent yarn ends.

TABLE III Fila- After boilefi Yarn ment Ten., Elong, 0d. denier RV g.p.d. percent g.p.d. BCE c.p.i."

e Denier per filament. b Yarn bundle crimp elongation. Crimps per inch (not extended).

carpet sections are prepared for each item having a pile height of about 0.5 inch (1.27 cm.). The carpet of Item A has a pile weight of 24 oz./yd.'-. (814 gm./m. The carpets of Items B and C have a pile weight of about 20 oz./yd. (678 gmjmeter The carpets are mock dyed as described previously and their floor soiling perform- Perrys Chemical Engineering Handbook, 4th edition, McGraw-Hlll 1963, pp. 5-21, Table 5-4.1, third equation (for rectangular shapes).

antisoiling nylon filaments which contain, after scouring, numerous discontinuous, microscopic voids.

The filaments of this invention provide better soiling performance and substantially equivalent bulk and durability in carpets as compared to solid trilobal filaments.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. As an article of manufacture, a continuous textile filament comprised of a thermoplastic synthetic polymer and characterized by a solid axial core and at least three substantially equispaced continuous nonround voids, a void content of from 10-35% and a cross-sectional contour substantially free throughout its periphery of abrupt radial departures.

2. The article of claim 1 wherein each void has adjacent boundary surfaces which are continuous and substantially plane and wherein said polymer is a composition selected from the group consisting of polyamides, polyesters and polyolefins.

3. The article of claim 1 wherein said filament has a nonround outline and said voids are substantially equidimensional.

4. The article of claim 3 wherein each void has a generally rectilateral outline and said filament consists essentially of polyhexamethylene adiparnide, said filament also having a generally rectilateral outline defined by flattened References Cited UNITED STATES PATENTS 2/1970 McIntosh et al. 161-178 OTHER REFERENCES Bohringer et al.: Development and Evaluation of Profiled Synthetic Fibers With and Without Hollow Core, Faserborschung nnd Teptiltechnik, 9, 405-416 (1958), No. 10, October.

DANIEL J. FRITSCH, Primary Examiner U.S. Cl. X.R. 

